Basically, all pistol cartridges need a crimp, since you bell the mouth of the case before bullet seating. Crimping removes the bell, and ensures a good tight fit. For bolt action and single shot rifles, a crimp is not necessary, since you don't bell. Friction fit of the bullet is normally tight enough. Accuracy may benefit or be hurt by crimping, just one of those quirks of reloading and your particular rifle. Lever action rifles with a magazine tube require crimping. The spring pressure of the follower, and the energy of recoil can actually push bullets farther into the case. If you're lucky enough to have a Browning or Savage lever action, then crimping will be optional. Ammo shot in a semi-auto should, as a general rule, be crimped. The cartridges get slammed around pretty hard during the cycle.
The vast majority of Lee bullet seating dies have a built in crimper. They do make a few that don't. Getting them to seat to the desired COL and crimp is a bit tricky, but doable. I use my seating dies for seating only, and then use a factory crimp die for my final operation. For my bolt action .223 I use Lee collet neck sizing die set, for my Mini-14 I use a full length resizing dies.
The vast majority of Lee bullet seating dies have a built in crimper. They do make a few that don't. Getting them to seat to the desired COL and crimp is a bit tricky, but doable. I use my seating dies for seating only, and then use a factory crimp die for my final operation. For my bolt action .223 I use Lee collet neck sizing die set, for my Mini-14 I use a full length resizing dies.